Add Slice 4 tuner stack with AGENTS-compliant core types and HTTP API.

Introduces Si4684/ADAU1701 drivers, TunerService, FrequencyKHz,
SeekDirection, /api/tuner routes without file-scope globals, host tests,
and firmware blob tooling (binaries remain gitignored).

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/components/drivers/si4684/CMakeLists.txt

@@ -1,6 +1,23 @@
+set(SI4684_FW_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../Firmware/Si4684-Firmware")
+
+if(NOT EXISTS "${SI4684_FW_DIR}/fm_firmware.bin")
+    message(FATAL_ERROR
+        "Missing ${SI4684_FW_DIR}/fm_firmware.bin — run:\n"
+        "  python3 tools/fetch_si4684_firmware.py --from-ugreen-radio-cli <Files_v16.zip>\n"
+        "  python3 tools/fetch_si4684_firmware.py --si46xx-dir <si46xx_firmware>")
+endif()
+
 idf_component_register(
-    SRCS "src/component_stub.cpp"
+    SRCS
+        "src/Si4684Driver.cpp"
+        "src/Si4684EmbeddedImages.cpp"
+        "src/Si4684Tuner.cpp"
     INCLUDE_DIRS "include"
+    REQUIRES core driver esp_driver_gpio esp_driver_spi
+    EMBED_FILES
+        "${SI4684_FW_DIR}/rom_patch_016.bin"
+        "${SI4684_FW_DIR}/dab_firmware.bin"
+        "${SI4684_FW_DIR}/fm_firmware.bin"
 )
 
 target_compile_features(${COMPONENT_LIB} PUBLIC cxx_std_23)